The relationships between sarcoma virus transformation and the expression of available membrane receptors for several polypeptide ligands were examined. Transformation of cells with either murine or feline sarcoma viruses specifically abolishes the binding of epidermal growth factor (EGF), a polypeptide growth factor, to its cellular membrane receptors. While the binding of three other polypeptide ligands, fibroblast growth factor (FGF), multiplication stimulating activity (MSA), and viral glycoprotein, to their membrane receptors were not decreased in murine or feline sarcoma transformed cells. Epitheloid and fibroblastic clones were isolated from the same source, a normal rat kidney line, and were characterized with respect to their polypeptide ligand receptors and the effect of sarcoma transformation on their expression. The epithelioid clones bound eight times more EGF per cell than the fibroblastic clones. Both cell types upon transformation showed a sharp decrease or a total loss of measurable EGF receptors. The fibroblastic clones, however, bound more MSA than the epithelioid clones, and the MSA binding was independent of murine or feline sarcoma transformation. BIBLIOGRAPHIC REFERENCES: De Larco, J. and Todaro, G.J.: Membrane receptors for murine leukemia viruses: Characterization using the purified viral envelope glycoprotein, gp71. Cell 8: 365-371, 1976. Fabricant, R.N., De Larco, J.E. and Todaro, G.J.: Nerve growth factor receptors on human melanoma cells in culture. Proc. Natl. Acad. Sci. USA 74: 565-569, 1977.